Interdigitated Back Contact Research Articles

Bifacial Perovskite/Silicon tandem solar cell with Ag nanoparticles as an intermediate layer

Abstract This study investigates a bifacial Perovskite/Silicon (PVK/Si) tandem solar cell with a four-terminal (4T) configuration using 3D simulation by finite element method (FEM). An intermediate layer containing Ag nanoparticles (NPs) is introduced between the sub cells in which the radius of 47.5nm achieved the best performance, balancing top and bottom cell absorption. The main purpose of using Ag NPs at the intermediate layer is to enhance the absorption and improve the electrical characteristics of PVK top cell. Implementing these optimized NPs resulted improvement of the top cell’s Jsc increment by 4.7% (reached 19 mA.cm-²), and power conversion efficiency (PCE) has been increased by 11% and reached 18.27%, compared to the cell without NPs. Following the optimization of the intermediate layer, the structural parameters of the bottom cell’s Interdigitated Back Contact (IBC) were investigated under global albedo reflection (0.3×AM1.5G). The optimal configuration for the bottom cell was achieved with Λ= 1mm, G/W= 2, resulting a Jsc of 20.78 mA.cm-² and a PCE of 11.5%. The final optimized structure exhibited a total PCE of 31.1%, representing an 11.5% improvement compared to the cell without albedo reflection.

Ultraviolet Laser Activation of Phosphorus‐Doped Polysilicon Layers for Crystalline Silicon Solar Cells

AbstractIn crystalline silicon photovoltaics (c‐Si PV), a pulsed laser can be used as a substitute for a high‐temperature furnace dopant diffusion/activation step. In contrast to furnace‐based activation, lasers can be used to achieve highly localized doping with controlled dopant concentrations, useful in advanced architectures such as the interdigitated back contact (IBC) solar cell. In this study, a pulsed ultraviolet (UV) laser is utilized for phosphorus dopant activation within a low‐pressure chemical vapor deposited (LPCVD) polycrystalline silicon (poly‐Si) passivated contact layer. The highest implied open‐circuit voltage iVoc values achieved using this approach reach 726 mV. However, this comes at the expense of high specific contact resistivities ρc, which is attributed to a lower dopant concentration across the poly‐Si(n+)/SiOx/c‐Si interface. Regardless, the optimum iVoc, ρc combination is measured at a laser fluence of 0.78 J cm−2 producing values of 712 mV and 89 mΩ‐cm2, respectively. These values are still compatible with high‐efficiency solar cell designs, underscoring the feasibility and effectiveness of this approach.

Systematic Modeling and Optimization for High‐Efficiency Interdigitated Back‐Contact Crystalline Silicon Solar Cells

This study utilizes Quokka3, an advanced solar cell simulation program, specifically tailored for interdigitated back‐contact (IBC) crystalline silicon (c‐Si) solar cells. Through meticulous Quokka3 simulations, the influence of several geometric and wafer characteristics of the solar cell backside on current–voltage (I–V) performance has been scientifically explored for IBC c‐Si solar cells. The investigation encompasses parameters such as wafer thickness, bulk lifetime, resistivity, emitter and back surface field area fraction, and front‐ and rear‐surface passivation. Optimal values for these parameters have been proposed to enhance the efficiency of IBC solar cells. These recommendations contain an emitter percentage of 70%, a wafer thickness ranging from 200 μm, a wafer resistivity of 1 Ω cm, and a wafer bulk lifetime of at least 10 ms. Moreover, under conditions where the cell is not short‐circuited, the potential for achieving higher cell efficiency, up to 26.64%, has been shown.

Performance Assessment of Cell-Separation Processes for Rear-Contact Solar Cells: Comparison of Indoor and Outdoor Measurements

Half-cell and third-cell modules are the current module technology standard due to their enhanced electrical performance. Also, special module layouts for building or vehicle integrated photovoltaics rely on non-standard cell formats obtained by separation techniques. For either application, interdigitated back-contact (IBC) solar cells are one of the promising cell technologies due to their higher performance and more aesthetic appearance. Thus, a cell separation process, usually employing laser tools, is needed that splits the cells as partial cells are manufactured from full cells. However, this cell cutting also induces additional electrical losses. In this work, we analyze the performance of third cell mini-modules made of IBC cells in comparison to PERC cells as reference. Under standard test conditions (STC), an overall performance gain can only be found for the PERC cells, while current and recombination losses dominate the IBC mini-modules. Outdoor measurements under non-STC conditions reveal reduced performance gains under lower illumination. We show a detailed analysis regarding the performance differences of the IBC and PERC cell technologies at indoor STC and outdoor non-STC test conditions.

The Electrical Contact Solution for Measuring Back Contact Solar Cells

Due to the cell design, it is challenging to measure back contact cells. In this study, we have designed and tested a contact chuck based on printed circuit board (PCB) technology. Both full cells and cut Interdigitated Back Contact (IBC) cells were tested and compared to a conventional spring-loaded probes based measurement chuck. Results show that IV parameters, especially fill factor (FF), can be measured with high accuracy and repeatability. In this case, the FF results are closer to the FF of modules. The chuck can also be used for other measurements, for example, electroluminescence and spectral response. The PCB layout can be adjusted according to the cell design, providing a more flexible, faster, and cost-effective approach than the traditional measurement chuck. The technology is suitable for measuring back contact cells in lab environments and in industry.

Evaluating the Practical Efficiency Limit of Silicon Heterojunction–Interdigitated Back Contact Solar Cells by Creating Digital Twins of Silicon Heterojunction Solar Cells with Amorphous Silicon and Nanocrystalline Silicon Hole Contact Layers

Improving power conversion efficiency (PCE) in photovoltaics has driven innovative approaches in solar cell design and technology. Silicon heterojunction (SHJ) solar cells exhibit advantages in PCE due to their effective passivating contact structures. SHJ–interdigitated back contact (SHJ–IBC) solar cells have the potential to surpass traditional SHJ cells, attributed to their advantage in short‐circuit current (JSC). Herein, Silvaco Atlas technology computer‐aided design is used to create digital twins of high‐efficiency SHJ solar cells with amorphous silicon and nanocrystalline silicon hole selective contact (HSC) layers. Using parameters from digital twins of SHJ solar cells, the practical efficiency limit of SHJ–IBC solar cells is assessed. The results show that SHJ–IBC cells can achieve potential efficiencies of 27.01% with amorphous HSC and 27.38% with nanocrystalline HSC. Further efficiency augmentation to 27.51% can be achieved by narrowing the gap from 80 to 20 μm. This study not only advances comprehension of SHJ–IBC solar cells but also provides insights into optimizing geometrical configurations for improved performance. The utilization of digital twins provides a valuable tool for predicting and evaluating the performance of SHJ–IBC solar cells, contributing substantively to the ongoing development of high‐efficiency photovoltaic technology.

Structuring Interdigitated Back Contact Solar Cells Using the Enhanced Oxidation Characteristics Under Laser‐Doped Back Surface Field Regions

Interdigitated back contact (IBC) architecture can yield among the highest silicon wafer‐based solar cell conversion efficiencies. Since both polarities are realized on the rear side, there is a definite need for a patterning step. Some of the common patterning techniques involve photolithography, inkjet patterning, and laser ablation. This work introduces a novel patterning technique for structuring the rear side of IBC solar cells using the enhanced oxidation characteristics under the locally laser‐doped n++ back surface field (BSF) regions with high‐phosphorous surface concentrations. Phosphosilicate glass layers deposited via POCl3 diffusion serve as a precursor layer for the formation of local heavily laser‐doped n++ BSF regions. The laser‐doped n++ BSF regions exhibit a 2.6‐fold increase in oxide thickness compared to the nonlaser‐doped n+ BSF regions after undergoing high‐temperature wet thermal oxidation. The utilization of oxide thickness selectivity under laser‐doped and nonlaser‐doped regions serves two purposes in the context of the IBC solar cell, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion. Proof‐of‐concept solar cells are fabricated using this novel patterning technique with a mean conversion efficiency of 20.41%.

Real-time and modelled performance assessment and validation studies of PV modules operating in varied climatic zones

With the increasing adoption of solar energy as a sustainable power source, it is crucial to evaluate the performance of photovoltaic (PV) modules under diverse environmental conditions to ensure optimal energy production and system efficiency. Present work gives a comprehensive overview of performance assessment and validation studies conducted on different PV module technologies such as multi-crystalline silicon (mc-Si), cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon (a-Si), heterojunction with intrinsic thin layer (HIT) and interdigitated back contact (IBC) operating under varied climatic conditions at different locations in India. To ensure accuracy and reliability, rigorous data collection and analysis methodologies were employed. The performance assessment has been computed through simulation using PVSOL software. Moreover, the performance ratio (PR) of all the PV module technologies was found to vary from 0.76 to 1.04. The present work validates the efficacy of the software as we have compared the computed results with real-time data obtained for all the PV modules, which were installed at NISE (National Institute of Solar Energy), Gurugram India. The performance ratio of all the PV module technologies has been evaluated through both the PVSOL and using real time data. The results show that the mean percentage change in PR values has been estimated approximately to be 2% in CdTe, CIGS, and a-Si modules technologies and 3% in mc-Si, HIT and IBC module technologies.

Process-induced losses by plasma leakage in lithography-free shadow masked interdigitated back contact silicon heterojunction architectures

Process-induced losses by plasma leakage in lithography-free shadow masked interdigitated back contact silicon heterojunction architectures

Stable passivation of cut edges in encapsulated n-type silicon solar cells using Nafion polymer

In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigitated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be “repassivated” after cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L&C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 °C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.

Optimising standard solar cell designs for maximum efficiency using genetic algorithms

ABSTRACT Solar energy is an alternative to conventional fossil fuels, and maximising the energy collected through solar cell design improvements is worthwhile. Genetic algorithms (GAs) have been historically useful in pursuing design improvements in solar cell architecture and manufacturing, particularly in combination with cell modelling software. This study demonstrates solar cell structural optimisation using PC3D software in combination with a genetic algorithm (GA) to maximise solar cell power conversion efficiency. PC3D is an Excel-based tool for modelling solar cells. The cell models examined here are: Passivated-Emitter Rear Contact (PERC), Interdigitated Back Contact (IBC), Aluminium-Back Surface Field (Al-BSF), and Passivated-Emitter Rear Locally Diffused (PERL). These are all silicon PV cells with varying structural features that significantly alter the performance of each cell. Absolute efficiency improvements of 2% for PERC, 1.6% for Al-BSF, 0.9% for IBC, and 0.5% for PERL cells are achieved. The main parameters impacting cell efficiency in this model are cell thickness and minority charge carrier lifetime, which feature a necessary trade-off between the higher absorption resulting from a thicker cell and the increased likelihood of charge collection arising from longer carrier lifetimes. These parameters are managed through other related values such as cell doping.

Mitigation of shunt in poly-Si/SiO passivated interdigitated back contact monocrystalline Si solar cells by self-aligned etching between doped fingers

Mitigation of shunt in poly-Si/SiO passivated interdigitated back contact monocrystalline Si solar cells by self-aligned etching between doped fingers

Interdigitated Back‐Contacted Carbon Nanotube–Silicon Solar Cells

Carbon/silicon heterojunctions provide a new perspective for silicon solar cells and in particular those made from carbon nanotubes (CNTs) have already achieved industrial‐level power conversion efficiency and device size when using organic passivation and a back‐junction design. However, the current state of the art device geometry for silicon photovoltaics is the interdigitated back contact (IBC) cell and this has yet to be demonstrated for CNT/Si solar cells due to the complexity of fabricating the required patterns. Herein, IBC‐CNT solar cells are demonstrated via the simple spin coating of a conductive hole‐selective passivating film and the evaporation of buried silicon oxide/magnesium electron‐selective contacts for both polarities. The CNT coverage area fraction (fCNT) and the gap between the two polarities are optimized to minimize electrical shading loss and ensure high photocarrier collection. Large‐area (4.76 cm2) highly efficient (17.53%) IBC‐CNT solar cells with a Voc of 651 mV and Jsc of 40.56 mA cm−2 are demonstrated and are prepared with one alignment step for the CNT/Si contact, and photolithographic‐free and room‐temperature processes. These performance parameters are among the best for solution‐processed dopant‐free IBC schemes and indicate the feasibility of using low‐dimensional carbon materials in IBC solar cells.

Photovoltaics literature survey (no. 182)

Photovoltaics literature survey (no. 182)

Nanopatterned SiNx Broadband Antireflection Coating for Planar Silicon Solar Cells

Crystalline Si solar cells based on thin wafers, with thicknesses in the range of 5–50 μm, can find applications in a wide range of markets where flexibility and bendability are important. For these cells, avoiding standard macroscopic texture is desirable to increase structural integrity. Herein, a nanopatterned SiN x antireflection (AR) coating that consists of 174 nm‐radius and 118 nm‐high SiN x nanodisks arranged in a square lattice on a thin (59 nm) SiN x layer is introduced. This geometry combines Fabry–Pérot AR and forward scattering by a resonant Mie mode to achieve high transmission into the Si absorber over a broad spectral band. The nanostructured coating is patterned on a commercial interdigitated‐back‐contact (IBC) Si solar cell, experimentally demonstrating a short‐circuit current density (J sc) of 36.9 mA cm−2, 2.3 mA cm−2 higher than for a single‐layer AR coated cell, and an efficiency of 16.3% at a thickness of around 100 μm. It is shown that light incoupling efficiency is comparable to that of pyramidal texturing, while the absorption in the infrared is lower, due to less‐effective light trapping. Overall, nanopatterned SiN x broadband AR coatings are an appealing option for improving light management in ultrathin solar cells and other optoelectronic devices.

A simplified and masking‐free doping process for interdigitated back contact solar cells using an atmospheric pressure chemical vapor deposition borosilicate glass / phosphosilicate glass layer stack for laser doping followed by a high temperature step

AbstractIn this paper a simplified approach for the generation of laterally p‐ and n‐doped structures applicable for cost‐effective production of interdigitated back contact (IBC) solar cells is presented. We use a stack of doping glasses deposited by atmospheric pressure chemical vapor deposition (APCVD), consisting of borosilicate glass (BSG) and phosphosilicate glass (PSG) on Czochralski‐grown (Cz) silicon substrates. A laser process creates the p‐doped regions by local liquid phase diffusion of boron from the BSG layer into the underlying molten Cz‐Si substrate. Simultaneously, the BSG‐PSG stack is removed by laser ablation. In a subsequent high‐temperature step, phosphorus diffuses from the remaining PSG‐BSG layer into the crystalline silicon substrate under inert gas atmosphere, creating complementary to laser doped areas n+‐doped regions. By the use of APCVD, phosphorus and boron contents of the doping glasses can be adjusted freely to vary the resulting p‐ and n‐doped profiles. A higher boron content in the BSG layer enhances the diffusion of phosphorus through the BSG, especially at lower diffusion temperatures. The resulting doping profiles are characterized using electrochemical capacitance‐voltage measurements and the resulting sheet resistances using the four‐point probe method. The amount of minority dopant contamination in n‐ and p‐doped regions is investigated by secondary ion mass spectrometry. Furthermore, transfer length method (TLM)‐measurements indicate contactability of the generated doped regions.

Over 700 mV IBC Solar Cell by Optimizing Front Surface Field Passivation

In this article, the front surface field (FSF) passivation of n-type interdigitated back contact (IBC) solar cell was studied and a method to improve the FSF passivation performance of n-type IBC solar cell was proposed. We optimized the phosphorus diffusion on the front surface of IBC solar cell to form a field passivation structure with low surface concentration and shallow junction depth. The surface recombination rate was calculated using EDNA2. Solar cell parameters were simulated by Quokka, and finally we did experiment verification. The results showed that when the deposition time and flow rate of POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> in the phosphorus diffusion process time is 3 min and POCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> flow rate is 80 sccm, the front surface saturation current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) is reduced to 3.71 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , corresponding to the front surface recombination rate of 100 cm/s. On solar cells, open-circuit voltage reached 704 mV, the average conversion efficiency of IBC solar cell exceeded 24%, and the highest conversion efficiency reached 24.28%.

Solution-processed PSS:MoOx composite thin film with triple function (passivation, antireflection, and hole-selective transport) for application in IBC solar cells

A novel solution-processed organic–inorganic composite material of poly(4-styrene sulfonic acid) (PSS) and molybdenum oxide (MoOx) nanoparticles is reported for use at the front of interdigitated back contact (IBC) solar cells as a triple-function layer.

Interdigitated Back Contact Technology as Final Evolution for Industrial Crystalline Single-Junction Silicon Solar Cell

We present our own Interdigitated Back Contact (IBC) technology, which was developed at ISC Konstanz and implemented in mass production with and at SPIC Solar in Xining, China, with production efficiencies of over 24%. To our knowledge, this is the highest efficiency achieved in the mass production of crystalline silicon solar cells without the use of charge-carrier-selective contacts. With an adapted screen-printing sequence, it is possible to achieve open-circuit voltages of over 700 mV. Advanced module technology has been developed for the IBC interconnection, which is ultimately simpler than for conventional double-sided contacted solar cells. In the next step, we will realize low-cost charge-carrier-selective contacts for both polarities in a simple sequence using processes developed and patented at ISC Konstanz. With the industrialisation of this process, it will be possible to achieve efficiencies well above 25% at low cost. We will show that with the replacement of silver screen-printed contacts by copper or aluminium metallisation, future IBC technology will be the end product for the PV market, as it is the best performing c-Si technology, leading to the lowest cost of electricity, even in utility-scale applications.

Detailed luminescence modelling in high-efficiency solar cells for precise calibration of spatially resolved characterisation methods: A bottom-up opto-electrical approach

In the scope of solar cell characterisation, spatially resolved imaging (SRI) methods (EL, PL and LBIC) have long been a standard procedure for valuable in-depth evaluation and extraction of various spatially resolved material properties, especially those related to the electrical behaviour. While this extraction can be straightforward in the case of laterally homogeneous devices, the situation is vastly different when the structural features are laterally varying, such as in the case of interdigitated back contact (IBC) solar cells. We show that in the case of laterally varying devices inherent device optical properties play a far more important role in determining the measured profile in this case and may indeed overshadow any underlying electrical effects. We therefore propose and validate a methodology that couples SRI characterisation with advanced bottom-up simulation of IBC solar cells. The method fully accounts for lateral device variability and allows for accurate extraction of the underlying electrical phenomena. We demonstrate the applicability of the method on state-of-the-art high-efficiency IBC solar cells, and explain the key factors, which could lead to misinterpretation of the results obtained solely by SRI measurements. • Interpretation of measured IBC electroluminescence profiles through opto-electrical simulation. • Decoupling of underlying optical and electrical phenomena. • Device optics overshadows recombination driven fluctuations of luminescence profiles. • Rear interface strongly influences the shape of the extracted luminescence profile. • Shape of the luminescence profile is highly dependent on imaging system’s aperture.